The studies of the action and activation of viral and cellular oncogenes represent a major focus in the current cancer research. Several approaches relying on in vivo virus infection or in vitro DNA transfection have been established; each has its own advantages and disadvantages. Recently we have developed a procedure whereby we can inject cloned DNA fragments directly into the wing-web of chickens and assess the in vivo sarcomagenic ability of the cloned DNA. We found that isolated v-src, the oncogene carried by Rous sarcoma virus can efficiently induce tumor nodules at the injection site, within two to three weeks. All the tumors analyzed have acquired v-src DNA in their genomes and express high level of v-src sequences. This conclusively shows that v-src alone without the help of other viral genes or viral infections, can trigger the sarcomagenic process. Interestingly, this sarcomagenic ability of v-src does not require the presence of a 5' promoter or LTR, but relies on downstream flanking sequences encompassing the enhancer region. We wish to substantiate these findings and extend our analysis to study the action and activation of other viral and cellular oncogenes. In particular, we describe detailed plans for studying the regulatory element involved in v-src activation and the oncogenic properties of c-src and c-fps/fes. Our approach, when fully developed, should not only open a new avenue for testing the sarcomagenic ability of isolated oncogenes but also provide means to study their regulations and mode of activations.